Circuit breaker having improved inductive heater for bimetal trip means



Aug. 3, 1965 c. E. GRYCTKO 3,198,905

CIRCUIT BREAKER HAVING IMPROVED INDUCTIVE HEATER FOR BIMETAL TRIP MEANS Filed Aug. 25. 1961 2 Sheets-Sheet 1 L I J INVENTOR.

0,424 5. wa er/r0 C. E. GRYCTKO CIRCUIT BREAKER HAVING IMPROVED INDUGTIVE HEATER FOR BIMETAL TRIP MEANS 2 Sheets-Sheet 2 Filed Aug. 25. 1961 I H I HN IN V EN TOR. 0,4,?! 5. w y/rm United States Patent O M CiRClUlT BREAKER HAVKNG IMPROVED INDUC- TlJE HEATER FGR BEMETAL TEE? MEANS Carl Gryctho, Haddon Heights, N.J., assignor to l-T-E Circuit Breaker Company, Philadelphia, Pa., 21 corporation of Pennsylvania Filed Aug. 25, 1961, Ser. No. 133,879 1 Claim. (Cl. 20t)88) This invention relates to circuit breakers in general and more particularly to an automatic tripping device therefor including a bimetal element and novel means for heating the bimctal by induction.

In automatic circuit makers, and more particularly molded case circuit breakers, the automatic tripping device usually comprises an instantaneous trip means in the form of a magnetic device and a time delay trip means in the form of a heated biinetal. For circuit breakers of relatively low current ratings, it is common practice to pass all circuit current directly through the bimetal for heating there of. However, for circuit berakers or" relatively high current ratings circuit current is passed through an indirect heater for the bimetal.

In the prior art the indirect heater usually comprised a current carrying member whose cross-section was reduced in the vicinity of the bimetal to cause heating in this area with the heat being transmitted to the bimetal element to cause deflection thereof. Another prior art indirect heating means comprised a current transformer designed in a manner such that circuit breaker current passed through the primary of the transformer. The transformer secondary comprised a shorted turn around the transformer core with the bimetal element connected to the secondary and in this manner being heated as a function of the current in the secondary.

As current ratings increased, the above noted prior art constructions have been found either to be impractical from a physical standpoint or the costs have been excessive. These problems have been overcome by the instant invention which provides means for heating a bimetal so that the circuit breaker conductor which carries circuit breaker current is of uniform cross-section throughout the length thereof. Because of this heat transfer to the external conductors is not impeded.

The basic concept underlying the instant invention is that effect often desired for inductive heating and as often not wanted in the vicinity of conductors carrying large values of current. Namely, the inductive effects on a closed magnetic path surrounding a current carrying conductor. Due to the flux surrounding the current carrying member, eddy currents are induced in the magnetic path with these currents producing heated areas in the iron member comprising the path which eventually appear as heat in this member. The bimetal element is in turn mounted directly to the iron member.

Accordingly, a primary object of this invention is to provide a circuit breaker having novel means for heating the time delay trip element.

Another object is to provide heating means of this type which does not require a reduction in cross section of the circuit conductors so as to permit heat generated in the circuit breaker at other points to be more readily conducted to the circuit breaker terminals and the external cables connected thereto.

Still another object is to provide a circuit breaker trip means in which the trip unit elements are of simple construction so as to require a minimum of machining.

A further object of this invention is to provide novel means for heating the bimetal element thereof with this means being such that heat generated thereby is isolated and can be insulated from the current carrying element of the circuit breaker.

Patented Aug. 3, 1965 These as well as other objects of this invention shall become readily apparent after reading the following description of the accompanying drawin s in which:

FIGURE 1 is a perspective illustrating the essentials of the instant invention.

FIGURE 2 is a longitudinal section of a molded case circuit breaker illustrating the current carrying path through the center phase of a typical three phase molded case circuit breaker with the time delay trip element thereof heated by the novel means provided by the instant invention.

FIGURE 3 is a plan view of the automatic trip elements of FIGURE 2.

Now referring to the figures and more particularly to FIGURE 1. Bar 11' corresponds to the current carrying strap of a typical molded case circuit breaker. Bar 11 passes through the central opening 12 of inductive heater 13 which comprises a closed loop of magnetic material such as soft iron. Rivets 14 fixedly secure one end of elongated bimetal element 15' to heater 13'.

The elongated bimetal element is cantilevered outward for the inductive heater 13', and freely extends beyond the boundaries thereof. The other end 16' of bimetal 15 is operatively positioned so that upon deflection of bimetal 15 caused by heating thereof end 16 will engage adjusting screw 17'. Screw 17 is carried by extension 18 of a tripper bar not shown which carries a circuit breaker trip latch (not shown). Engagement of screw 17 by bimetal 15' causes extension 18 to move the tripper bar and release the latch to bring about automatic tripping of the circuit breaker.

In operation, circuit breaker alternating current flowing through bar 11' along the path indicated by line A induces eddy currents within the magnetic material of the inductive heater 13'. These eddy currents cause heating of heater 13'. The heat generated being conducted to bimetal 15 with this heat causing the bimetal free end 16 to deflect toward screw 17'. With current in excess of a predetermined magnitude flowing through bar 11' bimetal 15 will be. sufiiciently heated to bring about automatic tripping of the circuit breaker in question.

FIGURES 2 and 3 illustrate a circuit breaker in which the time delay tripping element is heated by means constructed as in FIGURE 1. Circuit breaker 10 is typically a three phase unit including a molded housing comprising base 11 and removable cover 12 partitioned into three parallel elongated chambers with only the center chamber being illustrated. Each chamber houses identical current carrying elements, one for each phase of the circuit breaker, and in addition the center chamber houses a single contact operating mechanism 34 for all three phases.

Each of the current paths comprises load terminal connector 16, load terminal strap 17 having loop forming portions 18 and 2E lug 22, flexible member 23, movable contact arm 24, movable contact 25, stationary contact 26, line terminal strap 27 and finally tulip-type terminal connector 28 secured by screw 29 to line terminal strap 27. Arc chute 4b is positioned to receive electric current arcs drawn between cooperating contacts 25, 26 upon parting thereof.

Mechanism St for contact operation is of a type well known to the art and is completely described in the copending application of E. Wortmann, Serial No. 108,8l2, filed May 9, 1961, entitled, U-Shaped Cradle for Circuit Breaker. Briefly, operating mechanism 30 includes handle 98 which projects through cover opening 16-9 for manually operating cooperating contacts 25, 26 into and out of engagement. Handle 93 is mounted to the web of inverted U-shaped member 33 which is pivotally mounted at 32 to U-shaped frame 31. A pair of main springs 34 extend from the Web of U-shaped member 33 to tri- 3,1 3 angular member which is pivotally mounted to the knee 37 of the toggle linkage comprising links 38, 39.

The lower end of the link 39 is pivotally connected at 42 to bracket 43 which carries contact arm 24. The upper end of link 38 is pivoted at 41 to latchable cradle 50. Transverse tie bar 99 extends through all three of the housing compartments and carries the brackets 43 of all three phases so that the movable contacts 25 of all three phases are simultaneously operated into and out of engagement with their cooperating contacts 26.

Cradle carries latch member 51 engageable with portion 52 of auxiliary latch member 53 which is pivoted to frame 31 at 54. Latch tip 55' of auxiliary latch member 53 is engageable with main latch member 55 carried by transversely extending common tripper bar 56. When :tripper bar 56 is pivoted clockwise latch tip 55' is released, in turn releasing latch member 51 thereby permitting cradle 50 to pivot counterclockwise about its pivot 51a to collapse toggle 38, 39 so that springs 34 separate contacts 25, 26.

One part of terminal strap loop portion 18, 26 extends through U-shaped instantaneous trip magnet 61 which is secured to base 11 by screw 62. Instantaneous trip armature 63 is pivoted at its lower end against magnet 61 and is biased in a clockwise direction by tension spring 64, one end of which is connected to bracket lug 65 and the other end of which is connected to lug 66 of armature 63. When armature 63 is attracted by magnet 61 adjusting screw 67 carried at the upper end of armature 63 engages the downward extension 68 of tripper bar 56 to cause a clockwise rotation thereof for releasing of the circuit breaker latches.

Another part of loop portion 18, 20 extends through ring shaped inductive heater 70 which is secured to base 11 by screw 71. Insulating sheets 72, 73 insulate the heads of screws 62, 71, respectively from magnet 61 and heater 70, respectively. Screws '74, 75 rigidly secure the lower end of bimetal trip element 76 to heater '70. Bimetal element 76 cantilevers outward from closed loop heater 70 and freely extends beyond the boundaries of heater 70, towards tripper bar 56. The upper end of bimetal 76 carries adjusting screw 77 which is engageable with the upward extension 7 8 of tripper bar 56.

In a manner previously explained when describing the structure of FIGURE 1, circuit breaker current carried by load terminal strap 17 induces eddy currents to flow in heater 7%? which is constructed of ferromagnetic material. These eddy currents produce heating of inductive heater 70 with the heat being conducted directly to bimetal 76 causing a deflection thereof to the right with respect to FiGURE 2.

When the current through conductor 17 exceeds a predetermined value on a time-current basis, adjusting screw 77 will move suificiently to the right to engage tripper bar upper extension 78 causing tripper bar 56 to rotate clockwise thereby releasing the latches as previously explained.

At this time it is noted that terminal strap 17 is of uniform cross section throughout the length thereof. There is no need to reduce the cross section terminal strap in the region thereof adjacent to bimetal 76. Thus, conduction of heat, produced in housing 11, 12, to terminal connectors 16 and 28 and to the external conductors (not shown) will not be impeded. In addition, the heat generated in inductive heater 70 can be insulated from strap 17 either by interposing an air gap of sufiicient thickness or a thermal insulating member between strap 17 and inductive heater 70.

Thus, this invention provides a novel means in the form of a magnetic core inductively coupled directly to a circuit breaker conductor for heating of the bimetal trip element through the heat generated by eddy currents induced in the magnetic core.

Although I have here described preferred embodiments of my novel invention, many variations and modifications will now be apparent to those skilled in the art, and I therefore prefer to be limited not by the specific disclosure herein but only by the appending claim.

I claim:

A circuit breaker including a first and a second termi nal, means for connecting said terminals including cooperating contacts and a conducting strap serially connected to each other, a mechanism for operating said contacts into and out of engagement, and trip means connected to said mechanism for automatic tripping thereof upon the occurrence of predetermined abnormal circuit conditions, said trip means including a device inductively coupled directly to said strap and heated through the action or" current flowing in said strap; said device comprising a closed loop of magnetic material with said strap passing therethrough; said trip means also including a non-current carrying elongated bimetal element, a first end of said bimetal element secured to said closed loop in heat conducting relation thereto and the opposite end of said bimetal element cantilevered outward from said closed loop, and freely extending beyond the boundaries of said closed loop, towards said trip means; said opposite end operatively positioned for deflective engagement with said trip means; and calibrating means cooperating with said free end so that a predetermined heating of said element will bring about a deflection thereof sufiicient to trip said mechanism.

References Cited by the Examiner UNITED STATES PATENTS 2,170,412 8/39 Jennings 200116 2,340,957 2/44 Grissinger 200-88 2,824,922 2/58 ennings 200-116 2,921,169 1/60 Judd et al 200-153 2,939,929 6/60 Hobson 200l16 ROBERT K. SCHAEFER, Acting Primary Examiner. BERNARD A. GILHEANY, Examiner. 

